Poly(aryl ether sulfones) have been known for about two decades. They are tough linear polymers that possess a number of attractive features such as excellent high temperature resistance, good electrical properties, and very good hydrolytic stability. Two poly(aryl ether sulfones) are commercially available. A poly(aryl ether sulfone) is available from Imperial Chemical Industries, Ltd. It has the formula (1) ##STR1## and is produced by the polycondensation of 4,4'-dihydroxydiphenyl sulfone with 4,4,'-dichlorodiphenyl sulfone as described in, for example, Canadian Pat. No. 847,963. The polymer contains no aliphatic moeities and has a heat deflection temperature of approximately 210.degree. C. Another commercial poly(aryl ether sulfone) is available from Amoco Performance Products, Inc., under the trademark of UDEL.RTM.. It corresponds to formula (2), ##STR2## has a heat deflection temperature of about 180.degree. C., and is made via the nucleophilic polycondensation of bisphenol-A di-sodium salt with 4,4'-dichlorodiphenyl sulfone, as described in U.S. Pat. No. 4,108,837.
Over the years, there has developed a substantial body of patent and other literature directed to the formation and properties of poly(aryl ethers) (hereinafter called "PAE"). A broad range of PAE's was achieved by Johnson et al., J. of Polymer Science, A-1, Vol. 5, 1967, pp. 2415-2427; Johnson et al., U.S. Pat. Nos. 4,108,837 and 4,175,175. Johnson et al. show that a very broad range of PAE's including a large number of poly(aryl ether sulfones) can be formed by the nucleophilic aromatic substitution (condensation) reaction of an activated aromatic dihalide and an aromatic diol. By this method, Johnson et al. created a host of new PAE's.
Poly(aryl ethers) including poly(aryl ether sulfones) are generally prepared by the nucleophilic substitution reaction of an activated aromatic dihalo- or dinitro-compound with a dialkali metal salt of a bisphenol; or by the self-condensation of the mono-alkali metal salt of a halo- or nitrophenol, wherein the halo or nitro group is in a position ortho- or para- to an electron-withdrawing group such as the sulfone group. This process is described in the aforementioned U.S. Pat. Nos. 4,108,837 and 4,175,175. The polymerizations are generally performed in aprotic solvents.
Other variants of the nucleophilic aromatic substitution reactions are described in the following references:
Canadian Pat. No. 847,963 describes a process for preparing polyarylene polyether sulfones. The process comprises contacting equimolar amounts of a dihydric phenol and a dihalobenzenoid compound and at least one mole of an alkali metal carbonate per mole of dihydric phenol. The dihydric phenol is in situ reacted with the alkali metal carbonate to form the alkali metal salt thereof and the formed salt reacts with the dihalobenzenoid compound to form the polyarylene polyether sulfone in the usual fashion.
U.S. Pat. No. 4,176,222 describes the preparation of aromatic polyethers containing SO.sub.2 and/or CO linkages by a nucleophilic reaction utilizing a mixture of sodium carbonate or bicarbonate and a second alkali metal carbonate or bicarbonate. The alkali metal of the second alkali metal carbonate or bicarbonate has a higher atomic number than that of sodium. The second alkali metal carbonate or bicarbonate is used in amounts such that there are 0.001 to 0.2 gram atoms of the alkali metal of higher atomic number per gram atom of sodium. The process is stated to take place faster when the combination of sodium carbonate or bicarbonate and the second alkali metal carbonate or bicarbonate are used. Also, the products are stated to be of high molecular weight using such a combination.
U.S. Pat. No. 4,320,224 also describes the production of aromatic polyetherketones in the presence of an alkali metal carbonate or bicarbonate in an amount providing at least 2 gram atoms of alkali metal per mole of starting bisphenol. The patent states that the sole use of sodium carbonate and/or bicarbonate is excluded.
U.S. Pat. No. 3,941,748 describes the use of alkali metal fluoride for preparing polyarylethers. The process requires that sufficient fluoride be present so that the total fluoride available (including that from any fluoroaryl monomers) be at least twice the number of phenol (--OH) groups. The examples show it to be, in general, a slow process.
U.S. Pat. No. 4,169,178 refers to the British counterpart of U.S. Pat. No. 3,941,748, i.e., British Pat. No. 1,348,630. The patent states that the amount of alkali metal carbonate required may be reduced in the preparation of aromatic polyethers by employing fluorophenols or difluorobenzenoid compounds as part or all of the halogen-containing reactants. The patent states that the process gives faster reactions and higher molecular weights and less colored polymers than a process using potassium fluoride in place of potassium carbonate.
U.S. patent application Ser. No. 037,839, filed on Apr. 13, 1987 in the names of Paul A. Winslow, Donald R. Kelsey, and Markus Matzner, titled "Improved Process for Preparing Poly(aryl ethers) and Poly(aryl ether ketones)", commonly assiged, describes methods whereby high molecular weight, linear poly(aryl ethers) including poly(aryl ether sulfones) possessing excellent thermal stability and physical properties can be obtained at high polymerization rates. Specifically, the application is directed to an improved process for preparing poly(aryl ethers), poly(aryl ether sulfones, and poly(aryl ether ketones) by the reaction of a mixture of at least one bisphenol and at least one dihalobenzenoid compound, and/or a halophenol, in which the improvement comprises providing to the reaction medium, a combination of sodium or an alkaline earth metal carbonate and/or bicarbonate and a potassium, rubidium, or cesium salt of an organic acid or combinations of various organic salts thereof.
In another embodiment, the application is directed to an improved process for preparing poly(aryl ethers), poly(aryl ether sulfones), and poly(aryl ether ketones) by the reaction of a mixture of at least one bisphenol and at least one dihalobenzenoid compound, and/or a halophenol, in which the improvement comprises providing to the reaction medium a combination of sodium or an alkaline earth metal carbonate and/or bicarbonate and a lithium, sodium, or alkaline earth metal salt of an organic acid. In addition, this latter reaction can be catalyzed by the addition of a catalytic amount of a potassium, cesium, or rubidium salt catalyst. In this latter embodiment the process either does not make use at all of any added higher alkali metal compound (or compounds), contrary to the teaching in the prior art; or the process utilizes only catalytic amounts of higher alkali metal compounds which are substantially more effective than when used in prior art processes.
Moreover, all of the above variants may be advantageously performed in the presence of a small amount of cupric or cuprous ions.
In the preparations described hereinbefore, it is generally preferred to use either the chloro- or fluoro compounds as the activated halobenzenoid monomers. The chloro compounds are of interest because of their inexpensiveness. In some instances, however, the more expensive fluoro monomers have to be used. Such is the case when the electron withdrawing group is a relatively weak activating group (e.g., CO versus SO.sub.2); and/or when the diphenols used are relatively acidic whose anions are weak nucleophiles (e.g., 4,4'-dihydroxydiphenyl sulfone).
Poly(aryl ether sulfones) prepared by nucleophilic displacement polycondensation may contain both phenate and halo aromatic end groups, e.g., ##STR3## wherein X is a displaceable group such as halogen or nitro; M is the cation of the base used (e.g., Na.sup.+, K.sup.+, etc.) and Ar and Ar' are aromatic species. In the prior art, it has been customary to add a terminating agent, also referred to as an end-capping agent or end-stopper, at the end of the polymerization to react with the phenate end groups, e.g., EQU Polymer-O-Ar'-O.sup.- M.sup.+ +RX.fwdarw.Polymer-OAr'-OR.
For example, U.S. Pat. No. 4,108,837 illustrates in examples the use of methyl chloride as a terminating agent; U.S. Pat. No. 4,169,178 illustrates the use of dichlorodiphenylsulfone; and U.S. Pat. No. 4,320,224 illustrates the use of 4,4'-difluorobenzophenone as the terminating agent.
The use of an end-capping reagent can be useful for controlling the molecular weight of the polymer. However, more importantly, the presence of phenate or phenolic end groups in the polymer can lead to thermal instability. Converting these end groups to ether groups by use of an end-capping reagent results in generally improved thermal stability.
To assure that end-capping is complete, an excess of end-capping reagent is desirable, once the desired polymer molecular weight has been achieved; this, in order to assure that all of the residual phenate groups will react with the terminating reagent.
However, use of excess capping reagent can often lead to a significant decrease in molecular weight. This is known in the art; for example, U.S. Pat. No. 4,169,178 discloses that "end stopping may lead to some reduction in the polymer molecular weight". This patent illustrates in Examples 4, 6, and 7, for example, reductions in reduced viscosity of 0.11 to 0.29 within 5 to 10 minutes at 320.degree. C.-330.degree. C. after addition of a small amount of dichlorodiphenyl sulfone as the end-capping reagent.
This phenomenon has been confirmed in this application in Comparative Example A. The latter shows, that heating the poly(aryl ether sulfone) (1) in the presence of very small amounts of 1,4-bis(4-fluorobenzoyl)benzene and potassium fluoride in sulfolane, at 220.degree. C., for 0.5 hours decreases the initial reduced viscosity of the polymer from 0.47 to 0.28 dl/g.
Attwood, et al. [Polymer, 18, 359 (1977)], have discussed the problem of terminating polysulfones prepared from fluorophenyl-sulphonyl phenoxides with methyl chloride. They postulated a depolymerization due to potassium fluoride, a depolymerization which they depicted as follows: ##STR4## They suggested two methods to control the depolymerization during polymer termination:
(1) cool the reaction to "freeze" the equilibration by potassium fluoride before termination, or PA1 (2) polymerize beyond the desired molecular weight, isolate the polymer, and then degrade the polymer in dimethyl sulfoxide with sodium methoxide to the desired molecular weight and terminate with methyl chloride. PA1 (a) monovalent groups that activate one or more halogens or nitro-groups on the same ring such as another nitro or halo group, phenylsulfone, or alkylsulfone, cyano, trifluoromethyl, nitroso, and hetero nitrogen, as in pyridine. PA1 (b) divalent groups which can activate displacement of halogens on two different ##STR10## the azo group --N.dbd.N--; ##STR11## where R.sub.3 is a hydrocarbon group and the ethylidene group ##STR12## where A can be hydrogen or halogen.
Neither of the above methods is of practical interest. The first approach is generally not feasible because at temperatures at which termination proceeds effectively, equilibration often takes place as well, i.e., it is not totally supressed. On the other hand, the second approach given by Attwood et al. is cumbersome and, hence, expensive on a commercial scale.
Attwood et al. [British Polymer Journal, 4, 391 (1972)] also showed that polysulfones are cleaved at the ether linkage by fluoride ion; i.e., addition of potassium fluoride to a polysulfone resulted in re-equilibration to a lower molecular weight. With excess difluorodiphenyl sulfone also present, extensive depolymerization took place.